Tombolo

Last updated
Tombolo near Karystos, Euboea, Greece Tombolo Paximadhi Eboea.jpg
Tombolo near Karystos, Euboea, Greece
Tombolo contrasted with other coastal landforms. Accreting coast Image6.svg
Tombolo contrasted with other coastal landforms.

A tombolo is a sandy or shingle isthmus. A tombolo, from the Italian tombolo, meaning 'pillow' or 'cushion', and sometimes translated incorrectly as ayre (an ayre is a shingle beach of any kind), is a deposition landform by which an island becomes attached to the mainland by a narrow piece of land such as a spit or bar. [1] Once attached, the island is then known as a tied island.

Contents

Several islands tied together by bars which rise above the water level are called a tombolo cluster. [2] Two or more tombolos may form an enclosure (called a lagoon) that can eventually fill with sediment.

Formation

The shoreline moves toward the island (or detached breakwater) owing to the accretion of sand in the lee of the island, where wave energy and longshore drift are reduced and therefore deposition of sand occurs.

Wave diffraction and refraction

True tombolos are formed by wave refraction and diffraction. As waves near an island, they are slowed by the shallow water surrounding it. These waves then bend around the island to the opposite side as they approach. The wave pattern created by this water movement causes a convergence of longshore drift on the opposite side of the island. The beach sediments that are moving by lateral transport on the lee side of the island will accumulate there, conforming to the shape of the wave pattern. In other words, the waves sweep sediment together from both sides. Eventually, when enough sediment has built up, the beach shoreline, known as a spit, will connect with an island and form a tombolo. [3]

Unidirectional longshore drift

In the case of longshore drift due to an oblique wave direction, like at Chesil Beach or Spurn Head, the flow of material is along the coast in a movement which is not determined by wave diffraction around the now tied island, such as the Isle of Portland, which it has reached. In this and similar cases like Cádiz, while the strip of beach material connected to the island may be technically called a tombolo because it links the island to the land, it is better thought of in terms of its formation as a spit, because the sand or shingle ridge is parallel rather than at right angles to the coast.

Morphology and sediment distribution

Tombolos demonstrate the sensitivity of shorelines. A small piece of land, such as an island, or a beached shipwreck can change the way that waves move, leading to different deposition of sediments. Sea level rise may also contribute to accretion, as material is pushed up with rising sea levels. Tombolos are more prone to natural fluctuations of profile and area as a result of tidal and weather events than a normal beach is. Because of this susceptibility to weathering, tombolos are sometimes made more sturdy through the construction of roads or parking lots. The sediments that make up a tombolo are coarser towards the bottom and finer towards the surface. It is easy to see this pattern when the waves are destructive and wash away finer grained material at the top, revealing coarser sands and cobbles as the base.

Examples

Some of these may be simple isthmuses, and not have the deposition creation that defines a true tombolo. [7]

See also

Related Research Articles

<span class="mw-page-title-main">Beach</span> Area of loose particles at the edge of the sea or other body of water

A beach is a landform alongside a body of water which consists of loose particles. The particles composing a beach are typically made from rock, such as sand, gravel, shingle, pebbles, etc., or biological sources, such as mollusc shells or coralline algae. Sediments settle in different densities and structures, depending on the local wave action and weather, creating different textures, colors and gradients or layers of material.

<span class="mw-page-title-main">Lagoon</span> Shallow body of water separated from a larger one by a narrow landform

A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into coastal lagoons and atoll lagoons. They have also been identified as occurring on mixed-sand and gravel coastlines. There is an overlap between bodies of water classified as coastal lagoons and bodies of water classified as estuaries. Lagoons are common coastal features around many parts of the world.

<span class="mw-page-title-main">Chesil Beach</span> Shingle beach in Dorset, England

Chesil Beach in Dorset, England is one of three major shingle beach structures in Britain. Its name is derived from the Old English ceosel or cisel, meaning "gravel" or "shingle". It runs for a length of 29 kilometres (18 mi) from West Bay to the Isle of Portland and in places is up to 15 metres (50 ft) high and 200 metres (660 ft) wide. Behind the beach is the Fleet, a shallow tidal lagoon. Both are part of the Jurassic Coast and a UNESCO World Heritage Site, and together form an SSSI and Ramsar Site.

<span class="mw-page-title-main">Shoal</span> Natural submerged sandbank that rises from a body of water to near the surface

In oceanography, geomorphology, and geoscience, a shoal is a natural submerged ridge, bank, or bar that consists of, or is covered by, sand or other unconsolidated material, and rises from the bed of a body of water close to the surface or above it, which poses a danger to navigation. Shoals are also known as sandbanks, sandbars, or gravelbars. Two or more shoals that are either separated by shared troughs or interconnected by past or present sedimentary and hydrographic processes are referred to as a shoal complex.

Landforms are categorized by characteristic physical attributes such as their creating process, shape, elevation, slope, orientation, rock exposure, and soil type.

<span class="mw-page-title-main">Spit (landform)</span> Coastal bar or beach landform deposited by longshore drift

A spit or sandspit is a deposition bar or beach landform off coasts or lake shores. It develops in places where re-entrance occurs, such as at a cove's headlands, by the process of longshore drift by longshore currents. The drift occurs due to waves meeting the beach at an oblique angle, moving sediment down the beach in a zigzag pattern. This is complemented by longshore currents, which further transport sediment through the water alongside the beach. These currents are caused by the same waves that cause the drift.

<span class="mw-page-title-main">Longshore drift</span> Sediment moved by the longshore current

Longshore drift from longshore current is a geological process that consists of the transportation of sediments along a coast parallel to the shoreline, which is dependent on the angle of incoming wave direction. Oblique incoming wind squeezes water along the coast, and so generates a water current which moves parallel to the coast. Longshore drift is simply the sediment moved by the longshore current. This current and sediment movement occur within the surf zone. The process is also known as littoral drift.

<span class="mw-page-title-main">Barrier island</span> Coastal dune landform that forms by wave and tidal action parallel to the mainland coast

Barrier islands are a coastal landform, a type of dune system and sand island, where an area of sand has been formed by wave and tidal action parallel to the mainland coast. They usually occur in chains, consisting of anything from a few islands to more than a dozen. They are subject to change during storms and other action, but absorb energy and protect the coastlines and create areas of protected waters where wetlands may flourish. A barrier chain may extend for hundreds of kilometers, with islands periodically separated by tidal inlets. The largest barrier island in the world is Padre Island of Texas, United States, at 113 miles (182 km) long. Sometimes an important inlet may close permanently, transforming an island into a peninsula, thus creating a barrier peninsula, often including a beach, barrier beach. Though many are long and narrow, the length and width of barriers and overall morphology of barrier coasts are related to parameters including tidal range, wave energy, sediment supply, sea-level trends, and basement controls. The amount of vegetation on the barrier has a large impact on the height and evolution of the island.

<span class="mw-page-title-main">Coastal geography</span> Study of the region between the ocean and the land

Coastal geography is the study of the constantly changing region between the ocean and the land, incorporating both the physical geography and the human geography of the coast. It includes understanding coastal weathering processes, particularly wave action, sediment movement and weather, and the ways in which humans interact with the coast.

<span class="mw-page-title-main">Storm beach</span>

A storm beach is a beach affected by particularly fierce waves, usually with a very long fetch. The resultant landform is often a very steep beach composed of rounded cobbles, shingle and occasionally sand. The stones usually have an obvious grading of pebbles, from large to small, with the larger diameter stones typically arrayed at the highest beach elevations. It may also contain many small parts of shipwrecked boats.

<span class="mw-page-title-main">Presque-isle</span> Peninsula with narrow connection to mainland

Presque-isle is a geographical term denoting a piece of land which is closer to being an island than most peninsulas because of its being joined to the mainland by an extremely narrow neck of land.

<span class="mw-page-title-main">Paraguaná Peninsula</span>

Paraguaná is a peninsula and tied island in Venezuela, situated in the north of Falcón State, and comprises the municipalities of Carirubana, Los Taques and Falcón. The island of Aruba lies 27 km to the north. Bonaire and Curaçao are slightly further away. Paraguaná lies in the Caribbean Sea, and is connected to the rest of the state by the natural isthmus or tombolo of Médanos.

<span class="mw-page-title-main">Cuspate foreland</span> Geographical features found on coastlines and lakeshores

Cuspate forelands, also known as cuspate barriers or nesses in Britain, are geographical features found on coastlines and lakeshores that are created primarily by longshore drift. Formed by accretion and progradation of sand and shingle, they extend outwards from the shoreline in a triangular shape.

<span class="mw-page-title-main">Sedimentary budget</span>

Sedimentary budgets are a coastal management tool used to analyze and describe the different sediment inputs (sources) and outputs (sinks) on the coasts, which is used to predict morphological change in any particular coastline over time. Within a coastal environment the rate of change of sediment is dependent on the amount of sediment brought into the system versus the amount of sediment that leaves the system. These inputs and outputs of sediment then equate to the total balance of the system and more than often reflect the amounts of erosion or accretion affecting the morphology of the coast.

<span class="mw-page-title-main">Ayre (landform)</span> Shingle beaches in Orkney and Shetland

An ayre is the name used for shingle beaches found in Orkney, Shetland, the Isle of Man, Lancashire, Cumbria and Northumbria. The word is derived from the Old Norse eyrr, meaning a shingle beach or gravelly place, and may be applied to ordinary beaches, cliff-foot beaches such as the Lang Ayre in Northmavine, Shetland, spits, bars or tombolos, but only if formed of shingle. More than 130 such shingle beaches are named on Ordnance Survey maps of Shetland, but far fewer in Orkney, where most beaches are formed of sand. The word in its Old Norse form is common in Iceland, and it also occurs in a few place names in the north and west of the Scottish mainland which had a strong Norse influence, such as Eriboll and in the names of several shingle banks—Salt Ayre, Green Ayre, Stake Ayre, Rabbit Ayre and Whinny Ayre—in the tidal reach of the River Lune at Lancaster.

<span class="mw-page-title-main">Coastal engineering</span> Branch of civil engineering

Coastal engineering is a branch of civil engineering concerned with the specific demands posed by constructing at or near the coast, as well as the development of the coast itself.

<span class="mw-page-title-main">Tied island</span> Island that is connected to land only by a tombolo

Tied islands, or land-tied islands as they are often known, are landforms consisting of an island that is connected to the mainland or another island only by a tombolo: a spit of beach materials connected to land at both ends. St Ninian's Isle in the Shetland Islands off the north coast of Scotland is an example since it was once an island but is now linked to the mainland.

<span class="mw-page-title-main">Canterbury Bight</span> Oceanic bight in Canterbury, New Zealand

The Canterbury Bight is a large bight on the eastern side of New Zealand's South Island. The bight runs for approximately 135 kilometres (84 mi) from the southern end of Banks Peninsula to the settlement of Timaru and faces southeast, exposing it to high-energy storm waves originating in the Pacific Ocean. The bight is known for rough conditions as a result, with wave heights of over 2 metres (6.6 ft) common. Much of the bight's geography is shaped by this high-energy environment interacting with multiple large rivers which enter the Pacific in the bight, such as the Rakaia, Ashburton / Hakatere, and Rangitata Rivers. Sediment from these rivers, predominantly Greywacke, is deposited along the coast and extends up to 50 kilometres (31 mi) out to sea from the current shoreline. Multiple hapua, or river-mouth lagoons, can be found along the length of the bight where waves have deposited sufficient sediment to form a barrier across a river mouth, including most notably Lake Ellesmere / Te Waihora and Washdyke Lagoon

<span class="mw-page-title-main">Mississippi–Alabama barrier islands</span> Islands in the Gulf of Mexico

The Mississippi–Alabama barrier islands are a chain of barrier islands in the Gulf of Mexico along the coasts of Mississippi and Alabama enclosing the Mississippi Sound. The major islands are Cat Island, Ship Island, Horn Island, Petit Bois Island, and Dauphin Island; in the early 20th century the chain also included the Isle of Caprice, which has since been submerged. The islands are separated by wide inlets, several of which have been channelized to form the shipping channels for Gulf coast ports. The shapes and sizes of the islands have changed significantly since the 1800s, with the islands generally shrinking and shifting westward, especially after major tropical cyclones. Most of the islands are uninhabited. Much of the Mississippi portion of the chain is included in the Gulf Islands National Seashore.

References

  1. De Mahiques, Michel Michaelovitch (2016). "Tombolo". Encyclopedia of Estuaries. Encyclopedia of Earth Sciences Series. pp. 713–714. doi:10.1007/978-94-017-8801-4_349. ISBN   978-94-017-8800-7. Archived from the original on 2021-06-14. Retrieved 2021-04-05.
  2. Glossary of Geology and Related Sciences. The American Geological Institute, 1957
  3. Easterbrook, Don T. (1999). Surface Processes and Landforms (Second ed.). Prentice Hall. ISBN   0-13-860958-6.
  4. Neal, William; Orrin H. Pilkey; Joseph T. Kelley (2007). Atlantic Coast Beaches: A Guide to Ripples, Dunes, and Other Natural Features of the Seashore. Missoula, MT: Mountain Press Publishing Company. p. 272. ISBN   978-0-87842-534-1.
  5. Venancio, Kelly Kawai; Garcia, Patrícia Dalsoglio; Gireli, Tiago Zenker; Corrêa, Thiago Bezerra (2020). "Hydrodynamic modeling with scenario approach in the evaluation of dredging impacts on coastal erosion in Santos (Brazil)". Ocean & Coastal Management. 195: 105227. doi:10.1016/j.ocecoaman.2020.105227. S2CID   225314966 via ResearchGate.
  6. Brazilian Beach Systems. Coastal Research Library. Vol. 17. 2016. doi:10.1007/978-3-319-30394-9. ISBN   978-3-319-30392-5. S2CID   133158096.
  7. Owens, Edward H. (1982). Beaches and Coastal Geology. Encyclopedia of Earth Sciences Series. pp. 838–839. doi:10.1007/0-387-30843-1_474. ISBN   978-0-87933-213-6. Archived from the original on 2022-03-22. Retrieved 2021-04-05.